Diversity and characteristics of yeasts in water sources of the North West Province

Abstract

Yeasts form an important part of many ecosystems and significantly contribute to biodiversity. However, yeast biodiversity in the North West Province remains largely unexplored. The aim of this study was to determine the diversity and characteristics of yeasts from water sources in the North West Province, South Africa. Samples were collected over a two year period and included three rivers, a spruit and an inland lake. Temperature, pH, and electrical conductivity (EC) were measured on site using a multi-probe. Nitrate (NO3-N), nitrite (NO2-N) and phosphate (PO42-) levels were determined in the laboratory using Hatch kits and equipment. The pH ranged from 7.2 to 9.2. Elevated EC levels (36-70 mS) were detected especially at the Harts River and Barberspan (38-165 mS) sites. Physico-chemical parameter levels were higher during the cold dry sampling period compared to the warm rainy sampling period. Levels and diversity of yeasts were determined using the membrane filtration method. The highest level of yeasts was detected in the Mooi River and Schoonspruit during 2010 and 2011 sampling periods. Pigmented and non-pigmented yeasts were enumerated from all samples. Over the two year period the highest number of pigmented yeasts was detected in the Schoonspruit samples. In some cases there were significant (P<0.05) differences between pigmented and non-pigmented yeast levels among the sites. The diazonium blue B (DBB) test was carried out to distinguish between ascomycetous and basidiomycetous yeasts. These isolates were then identified using the API ID 32C system. Yeasts isolates were identified as belonging to the following genera: Candida, Cryptococcus, Pichia, Rhodotorula and Zygosaccharomyces. In addition using 26S rRNA gene sequencing Aureobasidium spp., Clavispora spp., Cystofilobasidium spp., Hanseniaspora spp., Meyerozyma spp., Sporidiobolus spp., and Wickerhamomyces spp.were also identified. The diversity and abundance of yeasts in the water sources demonstrated that opportunistic pathogens were present. This was supported by results that indicated some isolates could grow at 37°C and higher. In conclusion, our results provide preliminary information on the distribution and diversity of yeasts in water sources of the North West Province, South Africa.